This invention relates generally to record disc recording systems and more particularly to systems for recording signals with waveforms that produce no tracing and tracking distortion at the time of record disc reproduction.
In general, in a recording system for record discs, a cutting stylus records a signal in a groove of V-shaped cross section. In the reproducing system, the signal thus recorded is reproduced by a pickup reproducing stylus tracing the groove of the record disc. Since the tip of the reproducing stylus has a certain finite diameter, the locus or path of the center of the reproducing stylus differs from the path of the center of the cutting stylus. The reproduced signal thus acquires a tracing distortion, which causes a deterioration of the tone quality of the reproduced sound.
In a system known as a discrete 4-channel system, an angle-modulated wave difference signal is superimposed on a direct-wave sum signal, thereby to record a four-channel signal on a record disc. When there is a tracing distortion in the reproduced signal, there is both a deterioration in the tone quality of the reproduced sound, and an undesirable leakage of the direct-wave signal due to its cross modulation into the demodulated output of the angle-modulated wave. There is an interference of the distortion of the direct-wave signal with the angle-modulated wave signal, giving rise to abnormal noise in the demodulated output of the angle-modulated wave signal.
Accordingly, it is a general practice to impart a distortion into the recording sound signal. This distortion is opposite to the tracing distortion. The aim is to prevent the tracing distortion in the reproduced signal. This technique has been known in the prior art as, for example, the correlator system and the skew-sampling system.
However, none of these known systems for correcting tracing distortion has been successful in fully correcting tracing distortion. It has not been possible to completely prevent the occurrence of the above described difficulties accompanying tracing distortion.
The reason for this is that correction of tracing distortion has heretofore been carried out with attention concentrated only on making the motion of the cutting stylus coincident with the motion of the reproducing stylus. The premise has been that the waveform of the recorded signal and the waveform of the sound groove which has been cut are the same.
However, when the relationship between these waveforms was thoroughly studied, it was found that the recorded waveform does not coincide accurately with the waveform of the sound groove which has been cut. On the basis of this noncoincidence between the two waveforms, tracking distortion also occurs at the time of reproduction. Until now, however, this noncoincidence between the two waveforms merely has been pointed out. It has been overlooked in conventional 2-channel stereo systems, since it has no deleterious effect, in actual practice.
However, to attain reproduction of even higher fidelity, it is desirable to remove the above described tracing and tracking distortion. Furthermore, in discrete 4-channel systems, this tracing and tracking distortion gives rise to noise in the demodulated signal of the angle-modulated wave signal and has become a problem which cannot be neglected.